The present invention relates to electrostatic printheads and, more particularly, to the method of manufacturing electrostatic printhead portions having a row of dot-producing conducting printwire ends at a planar print face comprising, disposing a pair of printed circuit boards containing a plurality of parallel, spaced, flat, conductor strip ends along edges thereof in a common plane with the conductor strip ends disposed opposite one another in pairs; wire bonding connecting wires between the pairs of strip ends; embedding the connecting wires in an insulating material which will adhesively bond to the printed circuit boards along the edges thereof and cure into a hard material forming the body of the resultant printhead elements; and, cutting the cured insulating material between the edges of the printed circuit boards to form a pair of planar print face surfaces with the ends of the connecting wires exposed, thus producing two printhead portions each attached to a printed circuit board and having a single row of printwires at the print face thereof.
In an electrostatic printer, there is a printhead such as that generally indicated as 10 in FIGS. 1 and 2 comprising a body 12 of an insulative material having the exposed ends of a plurality of print wires 14 disposed in rows along the front surface 16 thereof. The other ends of the wires 14 emerge from the rear surface 18 and are used for electrically connecting the wires 14 to the driving circuits of the printer. For high resolution printing, the wires 14 may be 100-500 per inch and a typical printhead 10 in commercial electrostatic printers produced by the assignee of this application contains 14,080 print wires.
As depicted in FIG. 3, the most common technique presently employed in the art for electrically connecting the wires 14 to a printed circuit board 20 containing the connections to the driving circuits is to individually hand wire all 14,080 wires to the board 20. As can be appreciated, such hand wiring is very labor intensive and is economically feasible only by having the labor done in countries where lowcost manual labor is available. On the positive side, the hand wiring technique typically produces printheads with virtually no rejections; that is, if one of the wires 14 is not electrically connected as a result of a poor solder joint, or the like, the printhead is useless for commercial use unless and until the defect is found and corrected. Hand wiring generally avoids this problem since the wires are each given individual attention for soldering purposes and are visually inspected as part of that process.
In a co-pending application entitled ELECTROSTATIC PRINTHEAD AND APPARATUS by the applicant herein, and others, Ser. No. 086,919, filed Aug. 19, 1987, which is also assigned to the common assignee of this application, a novel method and apparatus for connecting the wires 14 to a printed circuit board(s) employing wire bonding techniques, in lieu of hand soldering, is described in detail. In one version as depicted in FIGS. 4 and 5, the wires 14 are cut off flush with the rear surface 16 and the connections between the wires 14 and a pair of printed circuit boards 20 (one for each of the two parallel rows of wires as shown in FIG. 1) are accomplished with wire bonding techniques which are well known in the art wherein fine gold or aluminum connecting wires 22 are bonded to the ends of the wires 14 and to the connectors (not shown) on the printed circuit boards 20 by electron beam welding, or the like, as symbolized by the arrows in FIG. 4. The two printed circuit boards 20 are then folded together by bending the connecting wires 22 as shown in FIG. 5. In an alternate version as depicted in FIG. 6, the rear surface 18 is cut into two levels and the connections between the wires 14 and a single printed circuit board 20 are again accomplished with wire bonding techniques wherein the connecting wires 22 are bonded to the ends of the wires 14 on the two levels and to the connectors (not shown) on the printed circuit boards 20 by electron beam welding, or the like, as again symbolized by the arrows in the figure.
While the automated connection methods and the accompanying apparatus taught by the above-referenced, co-pending application are a distinct improvement over the prior art hand-wiring method, the potential for improper or incomplete bonding to the ends of the wires 14 is a consideration of much importance, as can be appreciated from a detailed reading of that application. Since the bonding failure rate must be better than 0.007% (i.e. better than one wire in 14,080) sophisticated self-checking techniques must be incorporated into the wire bonding apparatus to correct any improper bonds at the time that they occur. Such equipment is, of course, complicated and expensive. It would be preferable to come up with a new design for electrostatic printheads, and the like, which could be formed quickly, easily, inexpensively, and reliably employing wire bonding techniques instead of employing wire bonding techniques as a substitute for hand soldering with the prior art approach to electostatic printhead designs.
Wherefore, it is the principle object of the present invention to provide a new design for electrostatic printheads, and the like, which can be formed quickly, easily, inexpensively, and reliably employing wire bonding techniques.
It is another object of the present invention to provide an automated method of connecting the wires of an electrostatic printhead to printed circuit board(s) with minimum potential for failed joints.
It is another object of the present invention to provide an automated method of forming the wires of an electrostatic printhead and connecting them to printed circuit board(s) employing wire bonding techniques.
It is still another object of the present invention to provide an automated method of forming an electrostatic printhead on the edges of printed circuit board(s) and for electrically connecting the printwires thereof employing wire bonding techniques.
Other objects and benefits of the present invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.